The present invention relates to nuclear magnetic resonance (NMR) spectroscopy and, more particularly, to improved methods for voxel localization in NMR spectroscopy procedures by use of a two-dimensional localization subsequence followed by a readout subsequence with a spatially-selective readout pulse for localization in the third of the three orthogonal dimensions.
It is highly desirable to be able to obtain high-resolution NMR spectra from a restricted region within a living organism, such as a human being and the like. Various detailed in vivo studies of molecular structure, concentration, metabolism, and the like, are possible if a volume element (voxel) can be precisely selected from a complex three dimensional sample. It is not only necessary to provide the voxel with well-defined boundaries, within which maximized sensitivity is present, but also to allow the selective volume to be easily moved within the sample. One common voxel-localization method is by restriction of the radio-frequency (RF) magnetic B.sub.1 field via the use of a RF surface coil; unfortunately, the sensitivity of the surface coil tends to be relatively coarse and maximized close to the surface of the sample. In any event, a highly desirable procedure presently appears to be: acquisition of an overall .sup.1 H image of the general volume of the sample; and electronic selection of the exact voxel, within that general volume, at which high-definition spectra are to be obtained. Unfortunately, many presently available techniques for achieving exact voxel selection, in spectral analysis, are highly susceptible to signal artifacts produced either by spurious physiological motion of the sample, during the sequence cycle, or by NMR relaxation occurring within a single acquisition sequence. The present invention is concerned with improved methods for spectral acquisition with volume localization and significant reduction of NMR signal artifacts.